Field effect transistors are used in a variety of electronic devices depending on their electrical properties, manufacturing processes, cost, etc. One kind of the field effect transistors, thin-film transistors (TFTs), is mainly used in liquid crystal display (LCD) screens as switching devices and driving devices. As such, switching speeds of the TFTs are critical.
Amorphous silicon TFTs, polysilicon TFTs and metal oxide TFTs are the most widely used TFTs. Amorphous silicon TFTs can be produced with low cost due to good uniformity of amorphous silicon films of large dimensions, but they suffer from relatively low mobility. Polysilicon TFTs have higher mobility compared to amorphous silicon TFTs, but their manufacturing processes are complex and they exhibit poor uniformity when applied to large panels. Metal oxide TFTs are viewed as candidates having potentials to replace amorphous silicon TFTs and polysilicon TFTs and have received lots of attentions.
It was found that epitaxial SnOx (x is zero or a positive number) films exhibit good p-type semiconductor characteristics and may function as a channel layer for p-type TFTs. However, it is difficult to produce high quality epitaxial SnOx films of large dimensions.
Moreover, sometimes complementary transistors (n-type and p-type transistors) are needed for periphery circuits outside pixel regions of the LCD screens. P-type transistors alone are hardly satisfactory.